Photographic printing system and method



Feb. 5, 1963 F- BIEDERMANN E AL 3,076,378

PHOTOGRAPHIC PRINTING SYSTEM AND METHOD Filed Oct. 15, 1958 Fig.7

2 Sheets-Sheet 1 [N V EN TOR.

Feb. 5, 1963 BIEDERMANN 3,076,378

PHOTOGRAPHIC PRINTING SYSTEM AND METHOD Filed Oct. 15, 1958 2Sheets-Sheet 2 IN V EN TOR.

United States Patent Oflice Fatented Feb. llfid 3,67 6,375 EilfilQG-RAPHKC i iilll l'lll l g SYSTEM AND METHQD Friedrich Eiedermann,hiuniclotlnterhaching, liticln ard Wish, Munich, Germany, assignors toFirina Agi'a Alrtiengeselischaft, Leverlrusen-Eayertverlr, Germany Filed65st. 15, E955, Ser- No. 763,521 (Ilaims priority, application GermanyGet. 23, 1957 it) Qlairns. {@i. hit-24) The present invention concerns aphotographic printing system, and more particularly to a system whichcomprises photoelectric means for automatically controlling and limitingthe exposure time used in the printing operation.

In the following specification and claims the element, usually anegative, from which the desired copy is printed, will be called imagecarrier, while the element on which the desired copy is photographicallyproduced, which is usually a photosensitive paper, film or the like,will be callec image receiver.

it is known that in using conventional photographic printing apparatusof the type mentioned above the exposure times to be used vary greatlydepending upon the average density or transparency of the image carrierso that, particularly when image carriers of extreme density are to becopied the so-calle Schwarzschild effect takes place as described forinstance in Handbuch der Kamerakunde, Verlag Luitpold Lang, Miincben,1954, page 190 and page 408.

Photographic printing apparatus with automatic ex posure control havebeen proposed which operate in such a manner: the exposure time is keptconstant while the intensity of the copying light is variedcorresponding to the density of the particular image carrier. By usingan apparatus of this particular type the above mentioned Schwarzschildeffect is eliminated but the constant exposure time must be chosen insuch a case to be so long that even image carriers or negatives of thegreatest density can still be printed with the copying light of themaximum available intensity. it can be seen that in this manner ofoperation the exposure time for image carriers of lesser or mediumdensity will be ex tremely long so that consequently the production timefor the photographic printing process is greatly extended. This iscertainly most undesirable and therefore the conventional printingapparatus cannot be considered to satisfactory in view of presentrequirements.

in view of this situation, it is the main obg'ect of this invention toprovide a photographic printing system and method which overcomes thedisadvantages of the liilOWIl apparatus and processes.

it is another object of this invention to provide a photographicprinting system and method which is comparatively simple and reliable,yet most economical particularly with respect to the required productiontime.

With above objects in mind, the present method and the photographicprinting ssern according to this invention mainly comprises, in additionto automatic photoelectri means for controlling limiting the exposuretime, additional photoelectrical control mea: s whici autorna callyadjust the illuminance produced by the light flux passing through theimage carrier and produced on the surface of the image receiver, to aselected normal value corresponding to a desired standard exposure time,yet compatible with the image-producing characteristics of the imagereceiver material.

It is to be understood that the above mentioned photoelectrical meanscorn, rise photo-responsive means as for instance a photocell, locatedin the path of the light radiation in an area beyond the image carrierso that the action of these photo-responsive means depends upon theilluminance produced on this photo-responsive means. As a rulephoto-responsive means for the above-new tioned purpose cannot be placedin the plane of the image receiver but will be suitably arranged eitherlaterally offset opposite the front face of the image receiver supportin which case the light reflected from tie surface of the latter or fromthe image receiver proper will impinge on the photo-responsive deviceand create a certain illurninance thereon, and, seen in the direction ofradiation, at a point beyond the image receiver so that in the systemaccording to the invention t e illuminance produced on thephotoresponsive device can be used instead of the actual illuminanceappearin on the surface of the image receiver, for deriving therefromthe required controls.

In a preferred embodiment of the invention the illumi nance produced onthe photo-responsive means, and thereby the illuminance appearing on theimage receiver, is automatically controlled. For this purpose, controlmeans depending upon the response of the photoresponsive means to theilluminance produced thereon, may comprise an clectromotor which isoperatively connected with means for adjusting the luminous fluxreaching the image receiver after passing through the image carrier. Theadjustment of the r'lurr may be carried out for instance by varyingemission intensity of the source of light, e.g. by changing the eiiectof an additional variable resistor in the circuit of said source oflight, through the operation of the above-mentioned motor. Preferably,however, the flux is adjusted by means of an adg'ustable light stop ordiaphragm incorporated in the optical system of the light source andoperatively connected with the above-mentioned motor.

Arrangements can be provided permitting to have the adjustment or" theluminous tluX carried out at a time before the exposure of the imagereceiver takes place in the actual printing operation, or so that theabovementioned adjustment takes place automatically during the exposureof the image receiver.

in a special embodiment of the invention as set forth theabove-mentioned photoresponsive means may consist in a photoelectriccell, the efiect produced thereby in response to the applied illuminancebeing used by both said first and second control means for carrying outthe adjustment of the luminous flux as well as the control andlimitation or" the exposure time, respectively. If both these controloperations are not to be carried out simultaneously then it is advisableto connect the photoelectric cell with switch means which permit toalternatively connect the photocell with either said first or saidsecond control means.

Usually photographic printing apparatus are provided with a switchingde' 'ce which permits altering of the emission intensity of the sourceor light from the value ordinarily used for the actual copying orprinting process, to a reduced value in fixed proportion therewith whichis preferably used in the period during which the image receiver isproperly located on some support-surface of the apparatus or otherwiseonly experimentally handled before the start of the actual exposure. Incertain cases it is advisable to connect the above-mentioned switchingmeans for the photocell with the switching means just mentioned forjoint operation so that the photocell can be electrically connected witha control means at the same time and by the same manual operation as theswitching means for altering the light intensity as mentioned above.

in a similar manner the switching means for altering the light intensityas mentioned above may be connected for joint operation with a switchcontrolling the operation of the above-mentioned electromotor.

It can be seen that a photographic printing system as provided by thisinvention entails substantial advantages aovaers" since the range ofexposure times required in printing from image carriers of variousdensities or transparencies can be substantially reduced on account ofthe proposed adjustment of the luminous flux which adjustment does noteven have to be extremely accurate. In this manner the so-callcdSchwarzschild effect is substantially eliminated hereby. In the courseof ordinary commercial operation of such printing devices handling imagecarriers of varying density the total of the exposure times is greatlyre duced as compared with those required in conventional apparatusoperating with constant exposure times. This is particularly truebecause the above-mentioned selected normal value of the illuminanceproduced on the surface of the image receiver, expressed in terms ofilluminance appearing on the photoresponsive means, to which the anparatus according to the invention is adjusted, can be chosen to becomparatively large. This will suflice for all ordinary cases. But evenin case the image carrier has an extreme density so that theabove-mentioned predetermined value of illuminance would still not besufficient on account of the great absorption of light in the imagecarrier, then the automatic control of the exposure time will stillserve to obtain entirely satisfactory prints or copies also in cases ofthis nature.

On the other hand by adjusting the luminous flux for an illuminance of aselected normal value a procedure is secured by which even in handlingimage carriers of little density or great transparency the exposure timewill not fall short of a certain desirable amount in spite of the smallabsorption of light in the image carrier. This just mentioned lowerlimit of the exposure time is mainly predetermined simply by the inertiaor time lag characteristic of certain relays used in the apparatus, andin the case of printing devices comprising means for additional lightexposure of the image receiver material for the purpose of obtainingdesired contrasts, the above-mentioned lower limit value of exposuretime is determined by the required time of applying the said additionallight exposure.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantage thereof, willbe best. understood from the following description of specificembodiments when read in connection with the accompanying drawings, inwhich:

FlGURE 1 is a diagrammatic schematic illustration of a photographicprinting system according to the invention, comprising means forautomatic control of the exposure time and automatic means for changingthe size of alight stop or diaphragm incorporated in the optical systemof the device; and

FEGURE 2 is a schematic electrical wiring diagram illustrating a circuitincorporated in the means for adjusting the aperture of the light stopor diaphragm shown in FIGURE 1.

Referring now particularly to FIGURE 1, an optical, i.e., enlargingtype, printing apparatus is shown as incorporating a lamp 1 constitutingthe source of light, a holding device 2 for receiving in sequence theparticular image carriers, and a projection system comprising objectivelenses 3, 4 whereby an accurately focused image can be produced on animage receiver (not shown) placed on the image receiver support 5.Between the lenses 5 and 4 an adjustable light stop, for instance aniris diaphragm 6 is arranged. The light source or lamp 1 can be operatedat two different emission intensities because the circuit connecting thelamp 1 with the general supply lines lit and ill includes two branches,one of which contains a light switch 3 while the other one contains aresistor 9. A change-over switch 7 is connected between said twobranches and the lamp 1, each of said branches ending in one of the twostationary contacts as and 2%. Therefore the switch 7 can be used foraltering the emission intensity of the lamp lby throwing this switchinto one or the other of its two positions. It is clear that theemission intensity will be lower when the switch 7 is in the positionshown in FIGURE 1, i.e., in series with the resistor 9.

The printing system as shown in FIGURE 1 further contains a controldevice 12 for automatically controlling or limiting the exposure timeand a second control device 13 for automatically controlling andadjusting the luminous flux caused by the emission radiation from thelamp 1, the device 13 controlling the iris diaphragm 6. Thelast-mentioned control devices 12 and 13 are also connected to andsupplied by the power lines 1t), 11. Either one of the control devices12 and 13 can be connected by means of a two-pole change-over switch l5,lid with a common photoelectric cell 14 which constitutes thephotoresponsive means of the system. As can be seen, the switch arm 15can alternatively contact either the sta tionary terminal 27 belongingto the control device 13 or the stationary terminal 30 belonging to thecontrol device 12, while similarly the switch arm in can in itsfirstposition contact the stationary terminal 28 of the device 13 and inits second position contact the stationary terminal 31 belonging to thecontrol device 12. The photoelectric cell 14 being preferably asecondary emission photomultiplier tube, is arranged in a predeterminedlocation within the path of the light radiation coming from the lamp 1,in this particular case in such a manner that light is reflected fromthe surface of an image receiver placed on the support surface 5, anddirected as a reflected beam onto the photocell 4; The control device 12for controlling or limiting the exposure time is not illustrated indetail because devices of this type are entirely conventional. it maysuffice to state that devices of this type include a time controlcapacitor the charge of which is influenced by the current derived fromthe cell 14, and a relay 1'? which controls the previously mentionedlight switch 8 by mechanical connections suggested by the dotted lineconnecting the relay with said switch.

A starter switch 32 is provided for closing the operative circuit of thedevice 12 and thereby to energize the relay l7 and to close the lightswitch 8, while the relay 17 is ale-energized and the light switch 8 isreturned to open position under the action of the circuit contained inthe device 12 under the influence of the photo cell 14- when theparticular image receiver has been sufiiciently exposed under theprevailing circumstances.

The second controldevice i3 is connected by conductors 18 and 19 with anelectromotor 2b which carries on its shaft 21 a gear 22 which, in turn,meshes with a gear 23 constituting the control ring of the irisdiaphragm 6. Consequently the aperture of the diaphragm 6 can beadjusted by the motor 2t) depending upon its direction of turn in such amanner that this aperture is either enlarged or reduced. A motor switch24- is provided in the connection 19.

As can be seen, in this preferred embodiment the switch arms 15, 16 aremechanically coupled with the motor switch 24 and also with theabove-mentioned change-over switch '7 of the lamp circuit, theconnection being illustrated diagrammatically by the dotted lines 25.Consequentlythe just-named switches can be operated jointly.

In operation, when the just-mentioned switches are in the position shownin FIGURE 1, i.e., if the photo cell 14 is connected with the secondcontrol device 13, the motor 2% being connected with the device 13 bythe closed switch 24, then the response of the photo cell 14 to theilluminance produced thereon by the reflected light as mentioned above,will influence the device 13 in such a manner that the motor 2i adjuststhe iris diaphragm 6 until through the corresponding adjustment of theluminous iiux the illuminance on the photo cell 14, or the relatedilluminance on the image receiver placed on the supports surface 5,reach, at least approximately, the above-mentioned selected normalvalue. Further details of an example of the control device 13 aredescribed further below with reference to FIGURE 2.

It can now be seen, that after the insertion of an image carrier ornegative into the holder 2 the emission intensity of the lamp 1 may bereduced so that the projection of the image onto the plane 5 can beexamined with respect to the accuracy of focusing, the quality of theimage in the image carrier and the quality of contrast thereof etc. Forthis purpose the switch 7 and together with it the switches 24 and l5,16 are in the position shown in FIGURE 1. Consequently, thephotoelectric cell 14 and the motor 26* are both connected with thecontrol device 13.

The illuminance produced on the photo cell M by the light rays reflectedby the image receiver on the surface 5 causes the photo cell 14 toproduce a current the strength of which has a predetermined relation tothe illuminauce produced by the light emitted by the lamp 2, and morespecifically to the luminous flux reaching the image receiver after thelight has passed through the image carrier and the aperture of the irisdiaphragm ti. It is to be noted that said values depend on th emissionintensity of the light source 1 which is now reduced at a fixed ratio bythe action of the switch 7 and by the fixed resistor 9. Now, due to theaction of the motor 2t? which is controlled by the device 13, the irisdiaphragm d will be adjusted until the current produced by the photocell 14 reaches a value which substantially corresponds to theilluniinance produced by the reduced emission intensity of the lamp 1 onthe surface of the image receiver placed on the support surface 5. Itmust be noted that depending upon the characteristics of the imagecarrier the iris diaphragm 6 will have to be either opened to a largeraperture or closed to a smaller aperture, from whatever previousaperture there may have existed, by the rotation of the motor in one orthe other direction. For obvious reasons the aperture adjustment of thediaphragm 6 is limited in both directions. It could well occur that inthe case of handling an image carrier of extremely great density theaperture of the diaphragm 6 is opened by produced on the image receiverfor causing the adjustment of the aperture of the diaphragm 6 is relatedto a predetermined value of emission intensity of the lamp 1 which isnot the same as the emission intensity to be used later during theactual printing operation when the efiiect of resistor Q is eliminated.

However it is evident that things can be arranged in such a manner thatthe reduced emission intensity determined by resistor 9 during theabove-described preliminary operation is in a fixed relation to theemission intensity used in the printing process, so that thecorresponding values or" the illuminances in either case also are in afixed relation. Thus it is pos- -,sible that the aperture adjusted inthe above ribed preliminary process is the correct aperture -for thesubsequent printing process.

Now the group of switches 7, 24 and 3.5, it may be swung into theiropposite positions so that the lamp 1 is now directly connected viaterminal 29 to the light switch 8 while the motor 24 is switched off sothat the adjusted aperture of the diaphragm 6 will not change any more,and moreover the photo cell 14 is connected by the switch arms l5, 16with the exposure time control device 12-.

It is quite feasible that in the above described operation no imagereceiver is placed on the support surface 5 so that the reflection fromthis surface instead of the reflection from the image carrier materialis being used for directing rays to the photo cell to. in that case nowthe photo receiver material is to be placed on the l ,o'tasrs supportsurface 5. In fact, this latter procedure will be the rule if imagereceiver material of comparatively high sensitivity is being used. inany case, now the starter switch 32 of the device 12 is operated wherebythe light switch 8 is closed through the action of the relay i! so thatthe exposure is started. Due to the previous adjustment of the apertureor" the diaphragm d the illuminance on the image receiver has new thepredetermined value. Should however, as described above, in the case ofan extremely dense carrier the opening of the aperature of the diaphragm6 have been limited by reaching its maximum, then at least theilluminance on the image receiver will be at a value which is as closeas possible to the predeterminec value thereof.

As soon as the required and predetermined amount of illumination hasbeen applied to the image carrier and thereby to the photo cell lid therelay It? will be deenergized in the well known manner of operation ofthe exposure time control device 32 so as to open the switch 8 wherebythe exposure is automatically terminated.

Referring now to FIGURE 2, a preferred embodiment of the second controldevice 13 is described in detail. A power supply unit of conventionaltype comprising a transformer 33, a rectifier 34 and the elements 35,as, 37 of a filter chain circuit is connected to a regular power supplyline 1%, 11 which furnishes alternating current. The necessary operatingvoltages for the cathode and anode of each of two control tubes 53, asare furnished via a voltage divider 3d, 39, il} through lines ll, 42.The control tubes 43:, 44- are pentodes the cathode heating coilswhereof are connected in a well known manner, not shown, with thealternating current supply. The tubes 43, 4 5 are supplied at theircontrol grids with approximately 1 volt AC. voltage by means of transformers 55, 4. When the arms 35, 16 of the abovedescribed changeoverswitch are in the position shown in the drawings, the photoelectric cell14 is connected with the stationary terminals 2'7, 23, respectively, ofthe device 13 and therefore constitutes together with the resistor 2-7 avoltage divider the junction point 45 between them constituting a centertap of the voltage divider which is connected with the control grid ofthe tube Therefore, depending upon the intensity of the current producedin the cell 314, the potential at the control grid of the tube isaltered so that the amplification produced by this tube iscorrespondingly changed,

A movable tap of the resistor Sil arranged in the anode circuit of thetube 4-3 is connected by the condoctor 51 with the control grid of thetube 4 so that the latter is controlled in a sense opposite to that ofthe tube 53-. Consequently, the more illuminance is produced on thephoto cell 14- the output AC. voltage of the tube &3 increases while theoutput voltage of the tube decreases. Thus, by adjustment of the tap thedevice 13 can be calibrated to the sensitivity of the image receivermaterial, and corresponding to the desired or selected normaliliuminance.

Between the cathodes and anodes of the control tubes 43, dd,respectively, are connected the primary winomgs of transformers 52, 5'3,respectively, which transform L14 anode voltages of the control tubes43, 54, respectively, and furnish the transformed voltages to therectifiers 54, 55, respectively. These rcctifiers are connected withphase shifting devices which comprise well known manner each a condenser56, 57, respectively, and a resistor 58, 59, respectively, the currentsupply being carried out by the secondary windings or the transformersas, til, respect'vely.

The two-phase sl ing devices are connected respectively with thyratronsd2, 63 which are connected with each other in anti-parallel relation,and both in series with the armature of the diaphragm adjustment motor26, and in series with the motor switch 24, the latter being connectedwith the secondary winding of the transacres-27s former 68. The cathodebias voltage for the thyratrons 62, 63 is obtained from the center taps64, 65, respectively, or" the secondary windings of the transformers 6d,61, respectively. The anode output voltages of the control tubes 43, 44are rectified by the rectifiers 54, 55, respectively, and aresuperimposed to the voltages derived from the phase shifting devices 56,'8 and 57, 59, respectively, and said superimposed voltages are thenfurnished to the grids of the thyratrons 62, as, respectively, via theconnections 66, 67, respectively. On account of the interpolation of theabove-mentioned phase shifting devices the grid and anode voltages ineach of the two thyratrons s2, 63 are out-of-phase with respect to eachother, preferably by 90.

By means of proper selection of elements or adjust- 'ment of adjustableelements shown but not described in detail the whole circuit is soadjusted that in the case or" an image carrier of average transparencyor density requiring for a desired standard exposure time acorresponding selected normal illuminance, adjusted by tap 49 to suitthe particular image receiver material, the anode A.C. voltages of thetwo control tubes 43, 44 are equal to each other. Therefore the twothyratrons 62, 63 carry currents which are of equal magnitudebutdirected opposite to each other. These currents compensate each other inthe motor circuit and have therefore no effect. The armature of themotor 20 which is actually a DC. motor with a permanent magnet field istherefore at rest.

In case a negative or image carrier of little density or little blackcontent is placed, into the support device 2 of the projector then theilluminance produced on the photoelectric cell 14 will be greater thanthe above mentioned selected normal illuminance whereby the potential atthe grid of the tube 43 is increased. Consequently the amplificationeffected by this tube increases and the anode voltage of the tube 43 andconsequently also the D0. grid voltage component of the thyratron 62 areincreased with the result that the ignition point of the thyratron 62 isreached later and the current passing through this tube 62 is reduced.At the same time the amplification of the control tube 44- is reducedwhereby the 11C. voltage component at the grid of the thyratron 63 islikewise reduced with the effect that the current through this tubeincreases. Now the current passing through the thyratron 63 is no longercompletely compensated by the oppositely directed current passingthrough the thyratron 62 so that the armature of the motor Zti willstart to rotate in one particular direction depending upon the directionof the dirlerence current and at a speed depending upon the strength ofthat current. Hereby the aperture of diaphragm d of the printingapparatus is reduced in the above-described manner until the illuminanceproduced on the photoelectric cell 14 is approximately reduced to theabove-discussed selected normal illuminance. In extreme cases it mayhappen that the aperture is reduced to complete closure thereof.

On the other hand, if the particular image carrier is rather dense or ofintense blackness with little transparency, the same control processdevelops except in the opposite direction.

It will be understood that the photographic printing system according tothe invention can be modified in various ways departing in certainrespects from the details of the embodiment illustrated in the drawings.For instance, the adjustment of the luminous flux from the lamp ll couldbe obtained by using instead of the iris diaphragm 6 a number ofadjustable light stops of a different kind, or by other suitable meansfor reducing the flux, among which may be a variable electricalresistance in the circuit of the lamp I, particularly in the branchthereof which contains the light switch 8. In such a case, the shaft 21of the motor 20 would have to be operatively connected with the movabletap of such a variable resistor.

Instead of using a motor 2i) and a motor controlled variable resistor inthe lamp circuit, the variation of the emission intensity of the lightsource may also be obtained by electronic means controlling the lampcurrent directly in response to the varying conductive condition orother effect of the photoelectric cell, a method which is known per seas being used in electronic light control equipment. Since in thisparticular case the variation of the emission intensity of the light canbe achieved without any time lag it is well possible to carry out theadjustment of the luminous flux instead of during the preliminaryoperations described above, simultaneously with the actual exposure ofthe image receiver.

While in the above-dmcribed embodiments of themvention one photoelectriccell 14 has been proposed for being used commonly and jointly for bothcontrol devices 12 and 13, the system is not basically changed ifinstead two separate photoelectric cells are provided one of which wouldbe associated and connected with the control device 12 while the otherone would be associated and connected with the second control device 13.

It should be further noted that it is quite possible to arrange in thepath or light radiation between the image carrier and the image receivera semi-transparent mirror for reflecting the light onto thephotoresponsive means. Particularly in this latter case it is possibleto mechanically connect the starter switch 32 with the switch 7 so thatthe exposure time control device 12 is automatically started the momentthe intensity of the light source 1 is switched from reduced intensityto full printing intensity. Of course, in that case the image receivermaterial must be placed on the supporting surface 5 before the switch 7is moved into the position shown in the drawings and the lamp 1 isswitched on to reduced intensity, and then the image carrier materialshould be covered in the preliminary operation of the lamp 1 at reducedintensity, for which the use of an automatically operating coveringdevice is advisable as it is known in so-called roll copying machines.Moreover, the starter switch 32 may also be operated by means of otherdevices forming part of the apparatus and having to be operated anywayduring the operation; for instance the switch 32 may be operatedautomatically by a cover which may be provided for temporarily coveringthe sup face 5.

While in all the embodiments described and mentioned reference has beenhad to a photographic printing device of the projector or enlarger type,it should be understood that the invention can be applied with the sameadvantageous efiects also to so-called contact type printing apparatus.The invention is also applicable to roll copy machines, particularly tothose which comprise a device for additional, uniform light exposure ofthe image re ceiver for the purpose of influencing the production ofsuitable contrast in the printed copy.

While in the above specification the means for adjusting the luminousflux have been described as operating automatically, it is stillpossible to modify the invention in such a manner that instead of theautomatic control of this adjustment means are provided which merely indicate when the desired and predetermined value of illuminance on theimage receiver is obtained. This means, that in this case the measurableeffect of the photoresponsive means is such an indication. In accordancewith the indication mentioned above the actual adjustment of theluminous flux will have to be carried out by hand separately, the meansof changing the ilux being of any one of the types described above. Theindicating means mentioned above could simply be a photoelectri-calexposure meter the indicating member whereof would have to be moved byadjusting the aperture of the diaphragm or by adjusting a resistor inthe lamp circuit until it registers with a fixed index or, in the caseof Working with image carriersof extreme density, would be caused tomove as closely as possible to such an index manic.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofphotographic printing systems d-ifiering from the types described above.

While the invention has been illustrated and described as embodied inphotographic printing system with automatic exposure time control, it isnot intended to be limited to the details shown, since variousmodifications and structural changes may be made without departing inany way from the spirit of the present invention as defined in theappended claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a photographic printing apparatus for producing photographicprints from transparencies on light-sensitive printing material, incombination,

(a) projecting means for projecting an image of a transparency to anarea at which a light-sensitive printing material is to be located so asto be exposed at said area to light passed through said transparency;

(1)) adjustable intensity varying means cooperating with said projectingmeans for adjusting the intensity of the illumination of said area, saidadjustable intensity varying means having a given range ofadjustability;

(c) adjusting means for adjusting said intensity varying means andincluding sensing means for sensing the intensity with which said areais illuminated by light passed through said transparency, said sensingmeans being operatively connected with said intensity varying means forautomatically adjusting the latter depending on said intensity so sensedso as to provide within said range of adjustability an intenstiy ofillumination at said area which with a given exposure time will providea given exposure; and

(d) timing means cooperating with said projecting means for providingsaid given exposure determined as the product of said adjusted intensityof illumination and said given exposure time, said timing means beingoperatively connected with said sensing means and controllable therebyfor providing said given exposure time in the case where thecharacteristics of said transparency are such that within said range ofadjustability of said intensity varying means it is possible to providesaid given exposure, and for providing, in the case where thecharacteristics of said transparency are such that within said range ofadjustability of said intensity varying means it is not possible toprovide said given exposure, an exposure time different from said givenexposure time and which with said intensity varying means at one end ofits range of adjustability will provide said given exposure.

2. Apparatus as claimed in claim 1, wherein said sensing means include aphotoelectric cell operatively connected with both said adjusting andsaid timing means.

3. Apparatus as claimed in claim 2, wherein said adjusting and timingmeans include switch means operatively connected with said photoelectriccell for alternatively connecting the latter with said adjusting andtiming means.

4. Appparatus as claimed in claim 3, including control means foraltering the intensity of said light passed through said transparency,and wherein said control means is coupled for joint operation with saidswitch means.

5. Apparatus as claimed in claim 2 wherein said adjusting means includeselectric motor means operatively connected with said intensity varyingmeans for adjusting the latter, and wherein said adjusting and timingmeans include switch means operatively connected with said photoelectriccell for alternatively connecting the latter with said adjusting andtiming means, said adjusting means including auxiliary control means forestablish ing the operability of said motor means, said auxiliarycontrol means being coupled for joint operation with said switch means.

6. In a photographic printing apparatus for producing photographicprints from transparencies 0n light-sensitive printing material, incombination,

(a) projecting means for projecting an image of a transparency to anarea at which a light-sensitive printing material is to be located so asto be exposed at said area to light passed through said transparency;

(b) adjustable intensity varying means cooperating with said projectingmeans for adjusting the intensity of the illumination of said area, saidadjustable intensity varying means having a given range ofadjustability;

(c) sensing means including at least one photoresponsive means forsensing the intensity with which said area is illuminated by lightpassed through said transparency;

(d) adjusting means for adjusting said intensity varying means andcontrollable by said sensing means for automatically adjusting saidintensity varying means depending on said intensity sensed by saidsensing means so as to provide within said range of adjustability anintensity of illumination at said area which with a given exposure timewill provide a given exposure; and

(e) timing means cooperating with said projecting means for providingsaid given exposure determined as the product of said adjusted intensityof illumination and said given exposure time, said timing means beingoperatively connected with said sensing means and controllable therebyfor providing said given exposure time in the case where thecharacteristics of said transparency are such that within said range ofadjustability of said intensity varying means it is possible to providesaid given exposure, and for providing, in the case where thecharacteristics of said transparency are such that within said range ofadjustability of said intensity varying means it is not possible toprovide said given exposure, an exposure time different from said givenexposure time and which with said intensity varying means at one end ofits range of adjustability will provide said given exposure.

7. Apparatus as claimed in claim- 6, wherein said adjusting means forautomatically adjusting said intensity includes electric motor means andadjustment means operatively connected with said intensity varying meansfor adjusting the latter.

8. Apparatus as claimed in claim 6, wherein said adjustable intensityvarying means comprises adjustable light stop means located in the pathof said light passed through said transparency.

9. Apparatus as claimed in claim 6, including means for changing theemission intensity of said light passed through said transparency fromthat used for the printing operation to an intensity being a fixedfraction of the former.

10. Apparatus as claimed in claim 6, wherein said adjusting and timingmeans are capable of operating simul taneously.

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1. IN A PHOTOGRAPHIC PRINTING APPARATUS FOR PRODUCINGPHOTOGRAPHIC PRINTSFROM TRANSPARENCIES ON LIGHT-SENSITIVE PRINTING MATERIAL, INCOMBINATION, (A) PROJECTING MEANS FOR PROJECTING AN IMAGE OF ATRANSPARENCY TO AN AREA AT WHICH A LIGHT-SENSITIVE PRINTING MATERIAL ISTO BE LOCATED SO AS TO BE EXPOSED AT SAID AREA TO LIGHT PASSED THROUGHSAID TRANSPARENCY; (B) ADJUSTABLE INTENSITY VARYING MEANS COOPERATINGWITH SAID PROJECTING MEANS FOR ADJUSTING THE INTENSITY OF THEILLUMINATION OF SAID AREA, SAID ADJUSTABLE INTENSITY VARYING MEANSHAVING A GIVEN RANGE OF ADJUSTABILITY; (C) ADJUSTING MEANS FOR ADJUSTINGSAID INTENSITY VARYING MEANS AND INCLUDING SENSING MEANS FOR SENSING THEINTENSITY WITH WHICH SAID AREA IS ILLUMINATED BY LIGHT PASSED THROUGHSAID TRANSPARENCY, SAID SENSING MEANS BEING OPERATIVELY CONNECTED WITHSAID INTENSITY VARYING MEANS FOR AUTOMATICALLY ADJUSTING THE LATTERDEPENDING ON SAID INTENSITY SO SENSED SO AS TO PROVIDE WITHIN SAID RANGEOF ADJUSTABILITY AN INTENSTIY OF ILLUMINATION AT SAID AREA WHICH WITH AGIVEN EXPOSURE TIME WILL PROVIDE A GIVEN EXPOSURE; AND (D) TIMING MEANSCOOPERATING WITH SAID PROJECTING MEANS FOR PROVIDING SAID GIVEN EXPOSUREDETERMINED AS THE PRODUCT OF SAID ADJUSTED INTENSITY OF ILLUMINATION ANDSAID GIVEN EXPOSURE TIME, SAID TIMING MEANS BEING OPERATIVELY CONNECTEDWITH SAID SENSING MEANS AND CONTROLLABLE THEREBY FOR PROVIDING SAIDGIVEN EXPOSURE TIME IN THE CASE WHERE THE CHARACTERISTICS OF SAIDTRANSPARENCY ARE SUCH THAT WITHIN SAID RANGE OF ADJUSTABILITY OF SAIDINTENSITY VARYING MEANS IN IS POSSIBLE TO PROVIDE SAID GIVEN EXPOSURE,AND FOR PROVIDING, IN THE CASE WHERE THE CHARACTERISTICS OF SAIDTRANSPARENCY ARE SUCH THAT WITHIN SAID RANGE OF ADJUSTABILITY OF SAIDINTENSITY VARYING MEANS IT IS NOT POSSIBLE TO PROVIDE SAID GIVENEXPOSURE, AN EXPOSURE TIME DIFFERENT FROM SAID GIVEN EXPOSURE TIME ANDWHICH WITH SAID INTENSITY VARYING MEANS AT ONE END OF ITS RANGE OFADJUSTABILITY WILL PROVIDE SAID GIVEN EXPOSURE.